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Preclinical studies with toremifene as an antitumor agent
S P Robinson1, C J Parker, V C Jordan
1Department of Human Oncology, University of Wisconsin Clinical Cancer Center, Madison 53792.
Abstract:
Toremifene is a nonsteroidal antiestrogen currently being evaluated for the treatment of breast cancer. Toremifene (10(-10)-10(-6) M) inhibited the growth of MCF-7 breast cancer cells in vitro but was ineffective against hormone-independent MDA-MB-231 cells. This activity was reproduced in vivo using the athymic mouse model. Maximal MCF-7 tumor growth was produced in athymic mice by circulating estradiol levels of approximately 200 pg/ml (from a 0.5 cm silastic capsule implanted sc). Toremifene (77 +/- 44 micrograms/day from a 2 cm silastic capsule) inhibited estradiol (0.5 cm capsule)-stimulated growth by more than 70%. No tumor growth was observed in mice treated with toremifene alone, although toremifene acted as a weak partial agonist and potent antagonist on the mouse uterus. The growth of MDA-MB-231 tumors was not influenced by either estradiol or toremifene. Toremifene (200 micrograms/day) was effective in preventing the development of 7,12-dimethylbenzanthracene-induced rat mammary tumors when given po from day 28 after carcinogen administration. The antitumor activity was reversed if the toremifene was stopped. These findings indicate toremifene is a tumoristatic agent rather than a tumoricidal agent. Clinical trials with toremifene should employ an indefinite treatment strategy to control tumor recurrence in adjuvant studies.
Insights
Toremifene effectively inhibits estrogen-sensitive breast cancer growth in vitro and in vivo. However, it acts as a tumoristatic agent, requiring continuous treatment to prevent recurrence.
Area of Science:
- Oncology
- Pharmacology
Background:
- Toremifene is an investigational nonsteroidal antiestrogen for breast cancer treatment.
- Estrogen receptor (ER) positive breast cancers are often hormone-dependent.
Purpose of the Study:
- To evaluate the efficacy of toremifene in inhibiting breast cancer cell growth in vitro and in vivo.
- To determine the mechanism of action and optimal treatment strategy for toremifene.
Main Methods:
- In vitro studies using MCF-7 (hormone-dependent) and MDA-MB-231 (hormone-independent) breast cancer cell lines.
- In vivo studies using athymic mouse models with MCF-7 and MDA-MB-231 xenografts.
- Evaluation of toremifene's effect on 7,12-dimethylbenzanthracene-induced rat mammary tumors.
Main Results:
- Toremifene inhibited MCF-7 cell growth in vitro and in vivo, but not MDA-MB-231 cells.
- Toremifene significantly inhibited estradiol-stimulated MCF-7 tumor growth in mice.
- Toremifene demonstrated preventive effects against carcinogen-induced rat mammary tumors, which were reversible upon cessation of treatment.
Conclusions:
- Toremifene exhibits tumoristatic, not tumoricidal, activity against breast cancer.
- Continuous toremifene treatment is crucial for managing tumor recurrence, particularly in adjuvant settings.